Polycyclic Scaffolds through the Intermediacy of Boron-Stabilized Nonclassical Carbocations
Ling Cheng1, Mingkai Zhang1, James P Morken1
1Department of Chemistry, Merkert Chemistry Center, Boston College, Chestnut Hill, Massachusetts 02467, United States.
None:
In the presence of catalytic amounts of Brønsted acid, boron-containing norbornene derivatives undergo a regioselective rearrangement to furnish boron-containing nortricyclanes. The unique stabilization of the putative 2-norbornyl cation by the boron substituent was investigated through both experimental and computational studies. Selective functionalization of the boronic ester product enables access to a diverse array of multisubstituted tricyclic structures, providing opportunities for broader applications.
Related Concept Videos
00:57Cationic Chain-Growth Polymerization: Mechanism
03:08Hydroboration-Oxidation of Alkenes
02:36Regioselectivity and Stereochemistry of Hydroboration
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.
02:10Carbocations
02:47Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
01:29Diels–Alder Reaction Forming Bridged Bicyclic Products: Stereochemistry